1. Technical Field
The invention relates to a wheel suspension for a vehicle comprising a transverse spring means, such as a leaf spring, in the longitudinal direction of the vehicle. The wheel suspension may be used advantageously both for front and rear suspensions.
2. Background Art
Modern wheel suspensions tend to become more and more complicated as demands increase for a comfortable ride and safe performance. Many known types of wheel suspensions are of the so-called multi-link type, which comprise a number of mutually connected pivotable linkages. By using an ingenious design of these linkages, it is possible to achieve an almost optimum compromise between, e.g., ride comfort and performance (such as cornering, rolling etc.) in accordance with the desired character of the vehicle. A disadvantage of this type of multi-link suspension is that the number of components, as well as the number of moving parts, are high, leading to higher costs that can only be justified for more expensive vehicles. The relatively large number of moving parts, such as ball joints, will eventually also entail higher maintenance costs due to wear.
For less expensive vehicles, it is therefore desirable to provide a wheel suspension having a simpler design, having as few moving parts as possible and manufactured at a lower cost while still fulfilling the requirements of ride comfort and performance necessary for this type of vehicle.
A problem with the simple wheel suspensions described above is that the limited cost margin and degree of complexity makes it difficult to achieve acceptable characteristics in view of roll damping and roll rigidity. For example, it is desirable to achieve a progressively stiffer suspension as the load on the vehicle increases.
A further problem with known wheel suspensions, such as the currently dominating so-called McPherson-type, is the use of bulky suspension struts with coiled springs that extend into the engine compartment, luggage compartment or passenger space of the vehicle, taking up valuable space that could be better utilized. The engine compartment in modern cars is often reduced by design limitations, which, together with increasing demand for engine performance, makes it desirable to maximize use of the available space for the engine and its peripheral equipment. With respect to the luggage compartment, the need for a low and level loading surface without extending struts is obvious.
A further problem with the known type of extending suspension struts is that their rigidity and upright position in the engine compartment present a potentially increased risk of injury to the body of a pedestrian, should a frontal collision occur in which the pedestrian strikes the hood of the vehicle. The hood itself, as well as other parts of the vehicle body, has been specially designed to absorb the energy of the collision by means of controlled deformation. At moderate speeds this results in a relatively gentle deceleration of the body of the pedestrian, as compared to the body of the pedestrian striking the relatively rigid suspension struts after an initial deformation of the hood. For this reason it is desirable to eliminate struts of this type from the engine compartment.
An early example of a simple wheel suspension using a transverse leaf spring is described in British Patent GB 264 074, published in 1926. Apart from being of a type that is unsuitable for modern vehicles for reasons of road-holding, this wheel suspension lacks roll inhibiting properties and progressively increasing roll rigidity.
A further example of a simple wheel suspension having a transverse leaf spring is taught in French Patent FR 2 632 573. This wheel suspension also lacks roll inhibiting properties and progressively increasing roll rigidity.
Finally, European Patent EP 0 195 536 discloses a simple wheel suspension having a transverse leaf spring, in which the ground clearance of the vehicle may be adjusted by manipulating one of the seats of the spring. However, progressively increasing roll rigidity can not be achieved.
The present invention solves the above problem by providing a wheel suspension for a vehicle having longitudinally a leaf spring or transverse spring means. This transverse spring means has a first end section positioned at the left half of the vehicle relative to a vertical longitudinal plane through the center of the vehicle, and a second end section positioned at the right half of the vehicle. Each end section is attached, either directly or indirectly, to a wheel carrier carrying the left and right wheels of the vehicle respectively at an outer attachment point relative to the longitudinal plane. The spring means is attached to the vehicle via a spring seat at an inner attachment point on either side of the plane. An upper deflection limiting device having a damper or engaging means for engaging said spring means is attached to the left and right half of the vehicle, respectively.
A particular feature of the invention is that the spring seats each comprise a lever that has a central suspension section with the lever pivotable relative to the vehicle around a suspension axis arranged in a substantially longitudinal direction of the vehicle. An inner end section is placed below and, in relation to the longitudinal plane, inside the central suspension section. At the inner attachment point the inner end section is provided with a supporting element that is in contact with the spring means. The supporting element is slidable along the spring means in the transverse direction of the vehicle as a function of the rotation of the lever around the suspension axis. An outer end section is placed outside the central suspension section. When the spring means contacts the engaging means of the deflection limiting device, an actuating device connected to the engaging means is arranged to mechanically act on the outer end section in such a way that the lever is rotated around the suspension axis, whereby the supporting element and the inner attachment point are displaced downwards and outwards towards the outer attachment point of the spring means.
According to a preferred embodiment of the invention, the outer end section is provided with an actuation surface arranged for contacting the actuating means.
Furthermore, the actuating means is preferably placed immediately adjacent the engaging means.
According to a further embodiment the spring means comprises a leaf spring.
According to an advantageous embodiment, the engaging means comprises a first liquid- or gas-filled hydraulic chamber that communicates with a second hydraulic chamber in the actuating means through a first conduit. The engaging means further comprises a first liquid- or gas-filled hydraulic chamber that communicates with a second hydraulic chamber, arranged in the actuating means, through a first conduit. The first hydraulic chamber preferably comprises an elastically compressible bladder, while the second hydraulic chamber preferably comprises an elastically expandable bladder.
Also, according to a preferable embodiment of the invention, a second intermediate conduit connects the first and second hydraulic chambers, wherein this second conduit is provided with a non-return valve preventing liquid or gas from flowing from the second hydraulic chamber to the first hydraulic chamber.
In a first alternative embodiment of the invention the actuating means comprises a hydraulic piston arranged to cooperate with the hydraulic chamber.
In a second alternative embodiment of the invention the engaging means comprises a hydraulic piston, while the actuating means comprises a liquid- or gas-filled hydraulic chamber in the form of an elastically expandable bladder arranged to cooperate with the hydraulic piston.
In a third alternative embodiment of the invention the engaging means comprises a first hydraulic piston, while the actuating means comprises a second hydraulic piston arranged to co-operate with the first hydraulic piston.
In a fourth alternative embodiment of the invention the engaging means is rigidly connected to the actuating means. The engaging means is spring loaded in a downward direction by means of a compressive spring, while the actuating means is spring loaded in an upward direction by means of a compressive spring.
In summary, the present invention offers a simple and cost-effective wheel suspension having a number of advantageous properties, such as automatic level control for a vehicle with a heavy load, automatic adjustment of the spring coefficient, and automatic control of the rolling rigidity.